Method of making a unitary brush head and unitary toothbrush head

ABSTRACT

A toothbrush comprised at least one unitary brush head having a base and at least one filament and extending therefrom and having a free end terminating with a tip, wherein the filament has a length of from 6.0 mm to 20.0 mm between the base and the free end, and wherein the unitary brush head is made from a plastic material that has a melt flow rate of not greater than about 30 g/10 min measured in accordance with ISO 1133.

FIELD OF THE INVENTION

The present disclosure is concerned with a method of manufacturing aunitary (i.e. single-piece) brush head comprising a base and filamentsextending from the base.

BACKGROUND OF THE INVENTION

It is known that a unitary brush head comprising a base and filamentsextending from the base can be manufactured by injecting molten plasticmaterial into a cavity defining the base and the filaments with arelatively high pressure and applying a holding pressure for a certaintime. Patent document U.S. Pat. No. 9,210,995 B2 generally describes aunitary brush head and its manufacture.

Simulations and experiments performed by the inventors have shown thatlong filaments with fine tips particularly suitable for, e.g., toothbrushing represent an issue for plastic injection molding, i.e. the finestructures may not be filled with the molten plastic as the frictionbetween the molten plastic material and the mold walls defining thefilaments is relatively high and causes freezing of the molten plasticsuch that the molten plastic completely solidifies before the finefilament structures are filled.

The present disclosure provides a method of making a unitary brush headsuch that also fine structures can be reliably filled that cannot bereliably filled with the known plastic injection molding technique.

SUMMARY OF THE INVENTION

In accordance with at least one aspect, a method of manufacturing aunitary brush head is provided, in particular a unitary toothbrush head,the unitary brush head having a base and at least one filament extendingfrom a filament side of the base, the method comprising the steps ofinjecting molten plastic material into a mold cavity having a pre-basecavity and at least one filament cavity extending from the pre-basecavity, in particular where the plastic material has a melt flow rate ofabout 30 g/10 min or lower measured in accordance with ISO 1133,compressing the molten plastic material once it is essentially fillingthe pre-base cavity by impressing at least one punching tool into themolten plastic material from the rear side of the pre-base cavity beingopposite to a side from which the at least one filament cavity extends,and filling the at least one filament cavity with the molten plasticmaterial under the continuous impression of the punching tool.

In accordance with at least one aspect, a brush is provided comprisingat least one unitary brush head having a base and at least one filamentextending therefrom in a unitary manner, wherein the at least onefilament has a length between the base and a free end of the filamentthat is in a range of between 6.0 mm and 20.0 mm, in particular in therange of between 7.0 mm and 15.0 mm, and the diameter of the filamenttip is in the range of between 5 μm and 40 μm, in particular in a rangeof between 8 μm and 30 μm, in particular where the unitary brush head ismade from a plastic material that has a melt flow rate of about 30 g/10min or lower measured in accordance with ISO 1133.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depiction of a toothbrush comprising a unitarybrush head.

FIG. 2 shows a simulated plastic flow into a cavity defining a unitarybrush head for plastic injection molding shown at a time instant wherethe plastic material is not yet completely filling the base cavity.

FIG. 3A shows a simulated plastic flow into a cavity defining a unitarybrush head for plastic injection compression molding shown at a timeinstant where the plastic material is not yet completely filling thebase cavity.

FIG. 3B shows a simulated plastic flow into a cavity defining a unitarybrush head for plastic injection compression molding shown at a timeinstant where a punching tool is completely immersed into the cavity andthe plastic material completely fills the base cavity and the filamentcavities.

FIG. 4 is a depiction of an incompletely injected unitary brush headmade with plastic injection molding.

FIG. 5 is a depiction of a completely filled unitary brush head madewith injection compression molding.

FIG. 6 is a depiction of a mold bar comprising two mold inserts.

FIG. 7 is a depiction of an exemplary mold insert assembled from a stackof insert plates.

FIG. 8 is a front view onto a front side of an example insert platestructured in accordance with the present description.

FIG. 9 shows a cross-sectional view of a moldbar having a mold insertand of a punching tool in a start position;

FIG. 10 is a depiction of an example filament of a unitary brush head;

FIG. 11A is a depiction of a moldbar comprising another embodiment of amold insert made from stacked insert rings; and

FIG. 11B is a depiction of a single exemplary insert ring.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure describes the manufacture of a unitary (i.e.single-piece) brush head comprising a base and at least one filament (inparticular a plurality of filaments) extending from the base. Thepresent disclosure also describes a unitary brush head and a brushcomprising at least one unitary brush head. As the unitary brush head isa single-piece object made in a single manufacturing step, the filamentsand the base are made from the same material and do not have any joiningline in-between, indicating that the filaments and the base are made insuccessive manufacturing steps. A unitary brush head may have a filamentdensity in the range of between 0.1 filaments/mm² and 5 filaments/mm²,in particular the filament density may be in the range of between 0.5filaments/mm² and 2 filaments/mm². The brush base area from whichfilaments extend may be in the range of between 1 mm² and 10.000 mm², inparticular in a range of between 10 mm² and 1.000 mm², and further inparticular in a range of between 50 mm² and 500 mm². A unitary brushhead in accordance with the present disclosure is in particular madefrom a plastic material having a melt flow rate of about 30 g/10 min orlower measured in accordance with ISO 1133. In case of a freedom ofchoice, the weight to be used in the measurement is a 2.16 kg weight.

It had been found that currently used plastic injection moldingtechnology is not suitable for reliable complete molding of finefilament cavity structures, but that injection compression molding tendsto be better suited to fill even the mentioned fine filament cavities.The term “fine” here is in particular directed to filaments having alength as is usual for brushing, in particular tooth brushing, i.e. in arange of between 3 mm and 20 mm, and a filament tip diameter in therange of below 50 μm or below 40 μm or below 35 μm or below 30 μm orbelow 25 μm or below 20 μm or below 15 μm, in particular being in therange of between 5 μm and 40 μm, further in particular in the range ofbetween 8 μm and 30 μm, and even further in particular in the range ofbetween 10 μm and 25 μm. This insight is the result of simulations andspecifically experiments, which are described further below. The presentdescription provides some examples of unitary brush heads suitable formanual toothbrushes, but other shapes and forms can be chosen so thatthe unitary brush head is suitable for, e.g., replacement brush headsfor electric toothbrushes (examples provided as well). It shall also notbe excluded that the unitary brush head can be used for other grooming,personal hygiene, or beauty applications such as hair brushing or for amascara brush. A filament tip may be flat or spherically rounded or mayhave a more irregular form. Where a flat filament tip is not circular,the filament tip diameter is defined by a best fit approximation of theflat filament tip with a circle (i.e. a circle for which the same areaof the non-circular shape lies outside of the circle as the area insidethe circle that is not filled by the non-circular shape—hence the bestfit circle has the same area as the irregular shape), where the diameterof the best fit circle is then determining the diameter of the flatfilament tip. The same can be applied to determine the diameter of afilament at a certain height level, where then a best fit of a circlewith the cross-sectional shape is done. Where the tip is not sphericallyrounded, the tip diameter is defined by a best fit approximation of thefilament tip with a half sphere, where the diameter of the best fitsphere is then the tip diameter. A further way to characterize the finefilaments that can be filled using ICM technology is given by the lengthof the filament between an intermediate diameter of a certain value andthe tip end. E.g. it had been found that a filament having a diameter of40 μm or below (which in other words shall mean a filament having a tipcross-sectional area of about 0.00126 mm²) and below can be filled overa length of 300 μm.

The unitary brush head as proposed herein has at least one filamentextending from a base in a unitary manner Consequently, the mold cavitydefining the unitary brush head comprises at least one filament cavity.In example embodiments, brushes for the mentioned applications have aplurality of unitary filaments, e.g. two filaments, five filaments, orten filaments. For toothbrushes, the number of unitary filaments may beat least 50 or at least 100 and further at least 150 filaments. Thenumber of filaments may be in the range of between 1 and 1000, inparticular in the range of between 5 and 500 and further in particularin the range of between 50 and 300. As will be discussed more in detail,each of the filaments may have the same filament geometry even though insome embodiments, at least one filament of the plurality of filamentshas a filament geometry different than the other filaments, and in someembodiments, each of the filaments has a filament geometry different toall other filament geometries of the filaments of the unitary brushhead.

In accordance with the present description, a method of making a unitarybrush head may comprise that the step of injecting the molten plasticmaterial into the pre-base cavity happens at a pressure that does notexceed the pressure at which the molten material would noticeably fillthe filament cavity (or the plurality of filament cavities). That meansthat the pre-base cavity is filled essentially without filling thefilament cavity. This step includes the sub-step of providing a pre-basecavity that has a larger volume than the base of the final unitary brushhead and the sub-step of impressing a punching tool into the pre-basecavity to—on the one hand—form the final base cavity and—on the otherhand—provide the necessary pressure for forcing the molten plasticmaterial into the fine filament cavities. The pre-base cavity has thus avolume that is given by the volume of the base cavity and the volume ofthe filament cavity (or filament cavities).

In some embodiments, the injection point at which the plastic materialis injected into the mold cavity is located sideways remote from the atleast one filament cavity so that the resulting flow direction of themelt is essentially perpendicular to the length extension of thefilament cavity or cavities when the melt reaches the filament cavity orcavities.

In some embodiments, the punching tool (e.g. punching stamp) has apunching surface that is impressed into the molten plastic material oncethe pre-base cavity is filled, which punching surface extends over thelocations of the plurality of filament cavities. This may generate amore homogeneous pressure in the melt, in particular as the moltenplastic does to some extent not behave like a Newtonian fluid.

In some embodiments, plastic materials suitable for the unitary brushhead have a maximum Shore D hardness of below about 70 and/or have atensile modulus of below about 1200 N/mm². It shall be understood thatthe maximum Shore D hardness is measured in accordance with ISO 868 at23 degrees Celsius and the tensile modulus is measured in accordancewith ISO 527 at 23 degrees Celsius as is usual and known in the art (ISOmechanical properties measured at 4.0 mm and specimen for ISO 527 is ISO1BA). In some embodiments, the Shore D hardness of the material is in arange of between 30 and 70. In some embodiments, the tensile modulus isin a range of between 100 N/mm² and 1200 N/mm², in particular in a rangeof between 500 N/mm² to 1000 N/mm², further in particular in a range ofbetween 700 N/mm² to 900 N/mm². The plastic material may in particularbe a thermoplastic elastomer or a thermoplastic urethane.

In some embodiments, the length of the filament cavity and hence thelength of the filament measured between base level and free end of thefilament is in a range of between 3.0 mm and 20.0 mm, in particular in arange of between 5.0 mm and 15.0 mm, further in particular in a range ofbetween 6.0 mm and 12.0 mm The filament may in particular be dividedinto a base portion and a tip portion, where the base portion and thetip portion may have similar or even identical length.

In some embodiments, a total minimum draft angle of the filament cavityin the range of between 0.4 degrees and 2.0 degrees, in particular ofaround 1.0 degrees, is achieved for at least half of the lengthextension of the filament cavity, in particular for a base portion ofthe filament. A tip portion may taper at larger angles towards the freeend of the filament in order to provide a fine filament tip.

The tip or at least one of the tips of a filament may have a diameter inthe range of between 5 μm and 40 μm, in particular in the range ofbetween 8 μm and 20 μm. At least one filament may have more than onetip, e.g. two, three, or four or even more tips. The tips may all lie onthe same plane parallel to the base plane or at least one of the tipsmay have a lower or higher lying tip end. E.g. in an example embodiment,a filament has two tips and the free end of the first tip may have aheight of about 8 mm above base level and the second tip may have aheight of about 10 mm above base level.

In the manufacturing of the unitary brush head, a mold insert (infollowing usually only named insert) may be used that is assembled froma vertical stack of at least two insert plates, where the filamentcavity is defined by either one depression in a face side of one insertplate (and a structure-less face side of the abutting other insertplate) or by two cooperating depressions in abutting face sides of theinsert plates. This shall not exclude that a projection or severalprojections may be formed on at least one of the face sides, whichprojection or projections extend into the cavity formed by thedepression to thereby shape the filament cavity. The term “vertical”here means that the filament cavity (filament cavities) is defined byabutting face sides of the insert plates instead of by through-holes(and potentially one blind end hole) in a horizontal stack of insertplates.

Generally, the use of a horizontal stack of insert plates is notexcluded for ICM-made unitary brush heads, but in the following, thepresent application focuses on a vertical stack of insert plates. Themore insert plates are used, the more filament cavity “rows” can bedefined. For a typical brush head size of between 1 cm and 3 cm inlength and width direction and a typical filament distance of 1 mm,about eleven to thirty-one insert plates may be used. In the presentdocument essentially planar insert plates are shown as one example andcircular insert plates (or insert rings) are shown as a second example.This shall not be limiting and otherwise curved insert plates arecontemplated as well. For planar insert plates, the filaments will bearranged in rows and for circular or ring-like insert plates, thefilaments will be arranged in rings.

For otherwise shaped insert plates, the filaments may be arranged onother lines (e.g. an ellipse or a wavy line). It is also contemplatedthat the insert plates have one curvature on one side and anothercurvature on the other side. Further, while the filaments shown in thepresent application all extend essentially perpendicular from the basesurface, at least one or several or even all of the filaments may extendfrom the base at an angle different to about 90 degrees (and inparticular, the angle and/or the direction of inclination may bedifferent between two or more of these inclined filaments).

In at least one of the insert plates, a venting cavity may be providedthat is in air-conducting connection with a blind-hole end of the atleast one filament cavity, which venting cavity has a thickness (i.e. anextension in vertical direction) in the range of between 2 μm and 20 μm,in particular in the range of between 3 μm and 10 μm, and further inparticular of about 5 μm. As the ICM technology described herein is ableto fill small filament tips, the venting cavity is chosen to be verythin so that the molten plastic material does essentially not enter intothe venting cavity. The thickness of the venting cavity may thus bechosen in view of the plastic material and its viscosity or melt flowrate.

The side faces of the insert plates may be pushed together duringoperation by a compression force to avoid that the pressure applied inthe compression stage pushes the insert plates apart. In someembodiments, the compression force is released prior to deforming theunitary brush head to ease the deforming step.

In accordance with at least one aspect, a method of manufacturing abrush is provided that comprises the steps of forming a unitary brushhead as discussed herein and connecting the unitary brush head with abrush handle, in particular where the brush handle is formed byinjection molding and further in particular wherein the connectionbetween the unitary brush head and the brush handle is established inthe injection molding step. The connection may be established bymaterial adhesion or by a form fit, where for the form fit the injectedmaterial of the brush handle flows into at least one undercut structureformed at the unitary brush head.

It shall not be excluded that at least one further cleaning element isconnected with the unitary brush head in a non-unitary manner, e.g. arubber-like cleaning element may be attached to the unitary brush head,e.g. by means of injection molding or mechanical connection. Further, itshall not be excluded that an already made brush head portion isprovided in the mold cavity as an insert element and that the unitarybrush head is then connected with this insert element in the injectioncompression process.

It shall be understood that a brush in accordance with the presentdisclosure comprises at least one unitary brush head. The brush head maycomprise two or more unitary brush heads that may be identical or thatmay differ from each other, e.g. they may differ in the color of theplastic material and/or in size, number of filaments, geometry of thefilaments etc. A brush may also comprise at least one further cleaningelement (e.g. a tuft of bristle filaments made by extrusion technology)that is attached to the brush by other known methods such as anchortufting (i.e. stapling) or hot tufting technologies (anchor-free tuftingtechnologies).

FIG. 1 is a schematic depiction of an example toothbrush 1 comprising aunitary brush head 2 having a base 3 and filaments 4 extending from thebase 3 in a unitary manner and a handle 5 that is connected with theunitary brush head 2. In the shown embodiment, the handle extendsunderneath the base 3 so that the head portion of the toothbrush 1 isformed by the unitary brush head 2 on the front side (where thefilaments are located) and a head portion of the handle 5. The handle 5may in particular be connected with the unitary brush head 2 in aninjection molding process, i.e. a process in which the unitary brushhead is inserted into a mold cavity and the handle is then injectionmolded and connects with the unitary brush head by materialadhesion/bonding (requiring respectively affinity between the materialschosen for the unitary brush head and the handle).

In the following, the simulation results of plastic injection molding(PIM) and of injection compression molding (ICM) of a unitary brush headis discussed with reference to FIGS. 2, 3A, and 3B.

Simulation of Plastic Injection Molding (PIM) and Experimental Results

In simulations (using the software tool “Moldflow” available from MFSoftware GmbH, Darmstadt, Germany) and respective experiments, thefilling of a unitary brush head cavity is investigated. The brush headcomprises a base and filaments extending at a 90 degrees angle from thebase. The base comprises a neck portion remote from the field offilaments. The molten plastic is injected into the neck section with atypical pressure and then flows towards the base portion from which thefilaments extend.

FIG. 2 shows a simulation result for a partially filled unitary brushhead cavity, where the molten plastic has not yet completely filled thebase portion of the cavity. The plastic material is injected via aninjection point on the left-hand side of the indicated cavity, whichinjection point is remote from the field of filament cavities. In theshown intermediate process stage, the molten plastic has already startedto flow into the filament cavities that extend from the base cavity. Itis now found that the plastic material in the partially filled filamentcavities may freeze (i.e. may solidify) under certain conditions so thatfurther filling of the thin filament cavities becomes essentiallyimpossible as the pressure required for filling increases exponentially.

In the simulations, Moplen HP 501M form Lyondell Basell, Huston, USA isused. This Moplen material has a melt flow rate (MFR) measured inaccordance with ISO 1133 at 230° C. with a 2.16 kg weight of 100 g/10min—hence, the Moplen material is a low viscosity and fast flowingmaterial. The maximum pressure that is applied to fill the filamentcavities is 470 bar (the simulation does not take into account anypressure losses in the hot runner system or the gating system).

The simulations are accompanied by experiments in which PIM is used tofill the unitary brush head cavity with the mentioned Moplen material.The experiments are performed with a brush head geometry comprising aregular rectangular arrangement of seven times twenty-six filaments (seeFIG. 4 for a depiction of an example unitary brush head made with PIMtechnology). In PIM, the molten plastic is usually pushed into the moldcavity at a relatively high pressure at which the filament cavities thatare first reached by the melt front are partially filled, where thefilament cavities that are reached at the end of the injection processare not filled to the same degree due to the pressure gradient in thefilling cavity. Once holding pressure is then applied, this highpressure drives the molten material into the remote filament cavities,but the plastic material that has flown in the filament cavitiesproximal the injection point has a certain probability offreezing/solidifying before the high holding pressure tries to drive themolten material into the filament cavities.

Simulation of Injection Compression Molding (ICM) and ExperimentalResults

In addition to the simulations and experiments of the plastic injectionmolding (PIM) of a unitary brush head, simulations and experiments areperformed with respect to injection compression molding (ICM) ofessentially the same unitary brush head cavity as discussed for PIM. Inthe ICM simulations and experiments, a punching tool is immersed intothe base portion of the unitary brush head cavity (as long as thepunching tool is not immersed into the cavity, the base portion of thecavity defines a pre-base and is thus named pre-base cavity).

FIG. 3A shows a simulation result of the ICM process (using again thematerial properties of Moplen HP 501M) at a point in time where thepre-base cavity is not yet completely filled with molten plasticmaterial. The molten plastic is essentially not flowing into thefilament cavities at this stage (which may essentially be because of thelarger cross-section of the pre-base cavity leading to a lower neededinjection pressure; a skilled person may experimentally confirm at whichpressure a given pre-base cavity can be filled without filling thefilament cavities for a given geometry and given plastic material). Oncethe pre-base cavity is filled, the punching tool (in the form of apunching stamp) is impressed into the pre-base cavity from a sideopposite to the side from which the filament cavities extend (thecompression phase of the process).

FIG. 3B shows the final stage at which the simulated punching tool is atits end position and the filament cavities are filled up to theirblind-hole ends even if very fine tip structures are chosen. The basecavity is thinner by the respective volume that is needed to fill thefilament cavities. The dimensions of the filament cavities are discussedin detail further below.

FIG. 5 shows a picture of an injection compression molded (ICM) unitarybrush head. It is confirmed by experiments that ICM is suited to fillthe fine filament cavities, in particular it is believed that this holdsfor plastic materials having a melt flow rate of below 30 g/10 minmeasured in accordance with ISO 1133 at 230° C. with a 2.16 kg weight,in particular for plastic materials having such a MFR of below 20 g/10min, further in particular of below 15 g/10 min. A lower value of 4 g/10min or 5 g/10 min may be chosen, but it is believed that it may berather difficult to fill the filaments with even lower MFR materials.

These low MFR plastic materials do not flow into the filament cavitieswhen the pre-base cavity is being filled, which enhances the effectalready provided by choosing a lower injection pressure than in PIM.While the higher MFR materials are preferred PIM materials as their“water-like” behavior allows a fast filling of the mold cavity, the more“honey-like” behavior of the low MFR materials can well be used in ICM,where a similarly fast filling of the mold cavity is not needed.Moldflow simulations and experiments show good agreement betweensimulated and experimentally found injection pressure and fillingdegree, even though the simulations seem to predict a higher filling ofthe fine filament cavities in PIM as can be proven in the experiments.

Materials used in the experiments include Hytrel 5553FG, Hytrel 6359FG(both Hytrel materials being available from DuPont, Wilmington, USA),and a mixture of 50% by volume Allruna W40D193 (available from ALLODWerkstoff GmbH & Co. KG, Burgbernheim, Germany) and 50% by volume MoplenRP2802 (available from Lyondell Basell, Houston, USA). The Hytrelmaterials have a Shore D hardness of 55 (Hytrel 5553FG) and of 63(Hytrel 6359FG). Further, Hytrel 5553FG has a tensile modulus of 170 anda melt flow rate of 7 g/10 min measured at a temperature of 230° C. witha 2.16 kg weight and Hytrel 6359FG has a tensile modulus of 260 and amelt flow rate of 9 g/10 min measured at 230° C. with a 2.16 kg weight.Based on objective hardness measurements and also based on subjectiveinvestigation of optical resetting properties of the ICM-made unitarybrush heads and based on practical use tests, Hytrel 6359FG is found tobe more suitable for tooth-brushing applications than the othermentioned materials. But it is believed that the filament geometry has agreat effect on the suitability of a given material. Generally, it isbelieved that plastic materials having a Shore D hardness of below 70tend to be better suitable than other plastic materials and/or materialshaving a tensile modulus of below 1200 N/mm² tend to be better suitable.These material parameters are in particular relevant for mechanicalperformance of the unitary brush head, e.g. wear and form stability.

Dimensions of the Filaments of a Unitary Brush Head

In the experiments mentioned above, two different filament geometriesare used to investigate the ICM technology. A first investigatedfilament geometry has a somewhat polygonal cross section at the basethat is defined by two triangles attached offset by 0.17 mm along oneedge, which base fit into a rectangle having a length of 0.9 mm and awidth of 0.69 mm This filament ends at a height of 10 mm above baselevel in two separate tips, where the triangular tips define a circleinside the tip triangle of 70 μm. A draft angle of 1.55 degrees is usedalong the full length of 10 mm.

A second investigated filament geometry (see FIG. 10 for a depiction ofthe respective filament) comprises a filament 60 of a total length of 10mm that is divided into a base portion 61 having a length of 5 mm and atip portion 62 having a length of 5 mm as well. The base portion 61 hasa quadratic cross-sectional shape on the base level of 0.5 mm times 0.5mm. The base portion 61 tapers on three sides with a draft angle of 0.5degrees. In the tip portion 62, the cross-sectional shape is reduced toa T-shaped cross section and the tip portion 62 tapers towards a flattip 63 of quadratic cross section having an edge length of 10 μm, i.e. across-sectional area of 10 μm times 10 μm=0.0001 mm² and a best-fitcircle diameter of 11.28 μm.

Generally, it is found that filaments, and hence the respective filamentcavities, may be divided into a base portion and a tip portion. In someembodiments, the base portion has a length of about 5 mm measuredbetween the base surface and the filament height t at which the tipportion starts, but the length of the base portion may lie in a range ofbetween 2 mm and 15 mm. The base portion may be designed to have across-sectional area at the base level in the range of about 0.1 mm² and5.0 mm², in , particular in the range of about 0.15 mm² and 2.0 mm², andfurther in particular in the range of about 0.2 mm² and 1.5 mm². In someembodiments, the cross-sectional shape of the base portion is quadraticor rectangular or circular or ellipsoidal/oval. The base portion mayhave a draft angle on at least one side in the range of between 0.2degrees to 2 degrees, in particular in the range of between 0.4 degreesto 1 degree. The tip portion may have a length of about 5 mm, but maygenerally have a length in the range of between 2 mm and 15 mm. The tipportion may taper much faster (i.e. at a greater angle) towards the tip.The tip end of the filaments may be flat or semispherical.

While not intended to be a limiting remark, filament geometries based ona frustum of pyramid (i.e. truncated pyramid) at the base of thefilament may be formed only into one side of an insert plate. Filamentgeometries based on a frustum of cone (i.e. truncated cone) at the baseof the filament may be formed in two oppositely arranged sides of twoinsert plates. As discussed before, other base portion geometries arepossible as well.

FIG. 6 is a depiction of a moldbar 300 having two inserts 320A and 320Bdisposed in a frame 310. The moldbar 300 will be inserted into a moldplate of a mold half of an injection molding machine. The shown moldbar300 is suitable for PIM and ICM. Each of the inserts 320A and 320Bdefines a first cavity portion 330A and 330B, respectively, of a unitarybrush head, where the first cavity portion 330A, 330B defines filamentcavities and at least a portion of the base (or-pre-base) cavity. While,in the present case, the moldbar 300 has two inserts 320A, 320B, amoldbar in general may have any other number of inserts, e.g., oneinsert, three inserts, four inserts, eight inserts, ten inserts, etc.

While it is described that the moldbar 300 is inserted into a mold plateof a mold half, more than one moldbar may be inserted into a mold plate,e.g., two moldbars, three moldbars, four moldbars, etc. While it is hereshown that the inserts 320A and 320B are essentially identical, each ofthe inserts of a moldbar may be different to the other inserts, i.e. maydefine a different unitary brush head. When several moldbars areinserted into one mold plate, each of the moldbars may be different fromthe other moldbars (i.e. may have a different number of inserts).Depending on the size of the unitary brush head, a single mold plate mayhave eight or ten or twelve or 16 or 20 or 24 or 32 or 64 etc. insertsso that in one single injection shot, the respective number of unitarybrush heads can be made. For sake of completeness, it shall not beexcluded that an insert is directly placed in a mold plate instead ofusing an additional mold bar. In a set of different moldbars, eachmoldbar may always have the same outer shape, but the different moldbarsmay comprise differently sized inserts. Hence, just the moldbar needs tobe replaced, but still the same moldplate can be used.

FIG. 7 is a depiction of an insert 400 that may be inserted into theframe 310 shown in FIG. 6. The insert 400 comprises a vertical stack ofinsert plates 410, 430, and 420. A plurality of structured insert plates430 is sandwiched between two end plates 410 and 420. In the shownembodiment, 27 structured insert plates 430 labelled 4301 to 4327 areused to define the filament cavities 431. The thickness of thestructured insert plates 430 may be in the range of between 0.7 mm to2.0 mm. A thickness of about 1.0 mm leads to a distance of the filamentsin vertical direction of 1.0 mm, which may be considered a sensiblevalue for a unitary brush head used for tooth brushing.

While the structured insert plates 431 shown have the same thickness invertical direction, the thickness of the structured insert plates mayvary, e.g., from 0.7 mm to 2.0 mm. While the structured insert platesshown have a first face side that comprises the structures defining thefilament cavities and a second face side without any structures, theinsert plates in general may include insert plates structured on bothface sides and/or may comprise non-structured insert plates, whichstructured and non-structured insert plates may be alternately arranged,but any other mixture of one-side structured insert plates, two-sidestructured insert plates, and not structured insert plates may be used.While the end plates 410 and 420 are shown as unstructured end plates,at least one of the end plates may be structured as well.

FIG. 8 is a front view onto a face side of a structured insert plate 800as may be used in an insert 400 as shown in FIG. 7 or an insert 320A or320B shown in FIG. 6. The insert plate 800 has a structured front faceside 801 and a further back face side 802 (not visible) that may bestructured but may as well be unstructured. The insert plate 800 has acut-out 820 in its top area 808, which cut-out 820 serves to define aportion of the base (or pre-base) cavity. Further, the insert plate 800has circular cutouts 830 and 831 that serve to align a plurality ofinsert plates by means of rod elements that in the assembled stateextend through the circular cut-outs 830 and 831, respectively. Aplurality of seven partial filament cavities 810 are provided in thefront face side 801 of the insert plate 800. In some embodiments, in anassembled state an unstructured face side of another insert plate abutsthe structured front face side 801 of the shown insert plate 800 and thepartial filament cavities 810 together with the unstructured face sideof the other insert plate define the respective filament cavities.

In some embodiments, the other insert plate comprises at least onepartial filament cavity that coincides in position with one of thepartial filament cavities 810 of the shown insert plate 800 and togetherform a filament cavity. Generally, a structured insert plate has atleast one partial filament cavity in one of its face sides (and hence, anon-structured insert plate has just plain face sides). While here aplurality of seven partial filament cavities are shown, any number ofpartial filament cavities may be provided in a structured face side ofan insert plate. Further, while here all partial filament cavities 810have the same form, at least one of the partial filament cavities mayhave a form different to the form of the other partial filamentcavities, and in particular all of the partial filament cavities may bedifferent to each other.

The shown embodiment indicates that the partial filament cavities 810are divided into a base portion 811 and a tip portion 812. The length ofthe base portion 811 and the length of the tip portion 812 may besimilar (i.e. the length of the base portion may be 40% or 60% of thetotal length of the partial filament cavity) or may be even identical.The base portion may have a total de-forming inclination angle (i.e.draft angle) of below 1 degree, whereas the tip portion 812 may tapermuch faster towards the blind-hole ends 813 of the partial filamentcavities. It had been found that such a divided filament cavitystructure, where the base portion stays essentially identical and thetip portion is then defining the particular structure of the filament tobe made tends to have good filling properties and good deformingproperties. The insert plate 800 further comprises a venting cavity 890that is provided in the front face side 801 of the insert plate 800. Theventing cavity 890 is in air-conducting connection with each of theblind-hole ends 813 of the partial filament cavities 810. The ventingcavity 890 may have a depth in the range of between 2 μm and 10 μm, inparticular in a range of between 3 μm and 7 μm, and further inparticular of about 5 μm. The venting cavity 890 may in particular bemade by laser ablation technology and in particular by application ofultra-short laser pulses. The venting cavity 890 has a very small depth.

As the ICM technology, as described, is suitable for filling thefilament cavities up the very front tip having a diameter in the rangeof between 40 μm down to about 5 μm, the air-conducting connection tothe venting cavity 890 had to be relatively thin (where the thicknessmay be chosen for a particular filament geometry and material—thethickness of the venting cavity used in the above described experimentsis 5 μm). Even under the high pressure applied by the punching tool asdescribed, the molten plastic material will essentially not enter intothe venting cavity 890 as the pressure required to fill this smallcavity is then too high. Obviously, even such a small connection betweenthe blind-hole ends 813 of the partial filament cavities 10 and theventing cavity 890 is sufficient for de-aeration of the filamentcavities in the assembled state.

Within the venting cavity 890 several stopper elements 891 are provided,where no material is ablated to form the venting cavity 890. In theassembled state and in use, the insert is held under pressure and theinsert plates may tend to deform and to enter into the small ventingcavities. This deformation is effectively avoided by providing thestopper elements 891. In the shown embodiment, venting channels 892connect the venting cavity 890 and the outside of the insert plate 800at the bottom area 809. The venting channels 892 may be made by anyconventional material ablation technology, which causes lower costs thanmaking a laser-ablated venting cavity 890 that extends to the bottomarea 809 of the insert plate 800.

FIG. 9 is a cross-sectional depiction of a moldbar 510 with mold insert520 defining in particular a pre-base cavity 530 and of a punching tool550 realized as a punching stamp that is arranged for being immersedinto the pre-base cavity 530 once it is filled with molten plasticmaterial in order to push the molten plastic into the fine filamentcavities 540. In the shown embodiment, the punching tool 550 hasessentially the same shape as the pre-base cavity so that the punchingtool 550 extends over all filament cavities 540. It is noted that forsake of presentability, the venting cavity at the end of the filamentcavities is shown with a dramatically increased depth. As previouslydiscussed, the depth of the venting cavity is in the range of a fewmicrometers.

In some embodiments, the punching tool is realized by one of the moldhalves and the mold halves are then moved relatively towards each otherto generate the needed pressure that drives the molten plastic into theat least one filament cavity. In some embodiments, the punching tool isan element that can be independently moved with respect to the moldhalves as is described.

In some embodiments, the pressure at which the molten plastic materialis injected into the mold cavity is chosen such that the at least onefilament cavity is essentially not filled, i.e. the injection pressureis chosen so low that the molten plastic material is not pushed into thefilament cavities. In other words, if a pressure value P is needed to atleast partially fill the filament cavity, than the pressure with whichthe plastic is injected into the base cavity is chosen such that thepressure in the molten plastic material at the location of the filamentcavity is below this pressure P. This assures that the molten plasticmaterial does not already solidify in the thin filament cavities priorto filling the whole filament cavity under the pressure of the punchingtool. While the molten plastic may form a thin skin of relatively coolplastic material extending over the filament cavities prior to immersingthe punching tool into the pre-base cavity, the high pressure exerted bythe punching tool will push the still liquid plastic material throughthe cooled skin into the filament cavities. Because of the sudden highpressure, the molten plastic material is filling the thin filamentcavity up to the small blind-hole end. In some embodiments, the at leastone filament cavity has a height in the range of between 3.0 mm and 20.0mm, in particular of between 8.0 mm and 12.0 mm, and has a blind-holeend diameter in the range of between 5 μm and 40 μm, in particular ofbetween 8 μm and 20 μm.

While here the term “blind-hole end” of the filament cavity is used,this shall not exclude that the filament cavity has a venting structurefor guiding air out of the filament cavity. Such a venting structure mayin particular have a venting cavity that is in air-conducting connectionwith the blind-hole end of the filament cavity. The thickness of theventing cavity at least at the location where the venting cavity is inair-conducting connection with the blind-hole end of the filament cavityis in the range of between 2 μm and 10 μm, in particular in the range ofbetween 3 μm and 7 μm, and further in particular of around 5 μm.

As mentioned before, the herein described method to manufacture aunitary brush head may be used to manufacture unitary brush headssuitable for replacement brushes for electric toothbrushes. Inparticular, a unitary brush head having a circular or elliptical/ovalshape may be made and may then be connected with a drive sectioncomprising a coupling portion. The filaments may be arranged on verticesof a rectangular lattice, as is previously described, or the filamentsmay be arranged in rings. For the latter arrangement, insert plates maybe provided having a circular or elliptical/oval shape (in particular,e.g. two semi-circular insert plates may form together a circular insertplate).

FIG. 11A is a top view onto a portion of an example mold bar 900comprising a mold insert 910 that comprises several essentiallyring-like (here: ellipsoidal) insert plates 920, 921, 922, 923, 924,925, and 926 that form a plurality of filament cavities 930 so that thefilaments are finally essentially arranged on rings. FIG. 11B is aperspective view onto a single example insert ring 950 that may be usedin a mold insert 910 as shown in FIG. 11A. The insert ring 950 comprisespartial filament cavities 960 and 961 formed on the outer face side 970of the insert ring and on the inner face side 971 of the insert ring950. As is shown in FIG. 11A, the partial filament cavities 960 and 961may cooperate with respective partial filament cavities in abuttingring-like insert plates to form the filament cavities for forming aunitary brush head. In the example shown in FIG. 11A, the symmetricallyarranged partial filament cavities of the stacked ring-like insertplates automatically align due to the ellipsoidal form of the insertplates. In case of circular insert plates, the insert plates may have atleast one cooperating groove and projection pair for aligning the insertplates. Again, while FIGS. 11A and 11B show insert plates having astructured outer and a structured inner side face, in other embodiments,only one of the side faces may be structured to form filament cavities.Essentially the same applies that is previously described in connectionwith the planar insert plates.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm”.

Every document cited herein, including any cross referenced or relatedpatent or application and any patent application or patent to which thisapplication claims priority or benefit thereof, is hereby incorporatedherein by reference in its entirety unless expressly excluded orotherwise limited. The citation of any document is not an admission thatit is prior art with respect to any invention disclosed or claimedherein or that it alone, or in any combination with any other referenceor references, teaches, suggests or discloses any such invention.Further, to the extent that any meaning or definition of a term in thisdocument conflicts with any meaning or definition of the same term in adocument incorporated by reference, the meaning or definition assignedto that term in this document shall govern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

1. A toothbrush comprising at least one unitary brush head having a baseand at least one filament and extending therefrom and having a free endterminating with a tip, wherein the filament has a length of from 6.0 mmto 20.0 mm between the base and the free end, wherein the unitary brushhead is made from a plastic material that has a melt flow rate of notgreater than about 30 g/10 min measured in accordance with ISO
 1133. 2.The toothbrush of claim 1, wherein the at least one filament has a tiphaving a diameter of not greater than about 40 μm for a length of atleast about 200 μm measured from the free end of the filament.
 3. Thetoothbrush of claim 2, wherein the tip has a diameter from 8 μm to 30μm.
 4. The toothbrush of claim 1, wherein the at least one filament hasa tip having a diameter of less or equal to about 40 μm for a length ofnot greater than 250 μm measured from the free end of the filament. 5.The toothbrush of claim 1, wherein the at least one filament has a tiphaving a diameter of not greater than about 40 μm for a length of atleast about 300 μm measured from the free end of the filament.
 6. Thetoothbrush of claim 1, wherein the toothbrush is made by a methodincluding the steps of: injecting a molten plastic material into a moldcavity having a pre-base cavity and at least one filament cavityextending from the pre-base cavity; compressing the molten plasticmaterial once it is essentially filling the pre-base cavity byimpressing at least one punching tool into the molten plastic materialfrom a rear side of the pre-base cavity being opposite to a side fromwhich the at least one filament cavity extends; filling the at least onefilament cavity with the molten plastic material under a continuousimpression of the punching tool.
 7. The toothbrush of claim 1, whereinthe plastic material comprises a thermoplastic elastomer or athermoplastic urethane having a Shore D hardness of below about 70measured in accordance with ISO 868, and wherein the plastic materialhas a tensile modulus of below about 1200 N/mm² measured in accordancewith ISO 527.